Ultra-low frequency dynamic strain detection with laser frequency drifting compensation based on a random fiber grating array

Abstract The measurement of dynamic strains of both high and low frequency give rise to a variety of problems in instrumentation. Two types of equipment and circuits designed and used by the authors are discussed in detail. The first type based on the amplitude-modulated method is for low frequencies from zero to about 15 per cent of the carrier frequency of 1025 cycles per sec. The equipment has application to strain measurements varying from static values to those produced in moving vehicles, various machine parts, structures such as crane bridges, in fact all strain measurements where the frequency is 150 cycles per sec or less. The second type of equipment discussed is a potentiometer type and is for high-frequency strain measurements from 100 cycles per sec to 8000 cycles per sec. This high-speed equipment is conveniently used for impact strain, such as produced in hammer blows, shock loading, forging equipment, and impact-factor determination. Both units are designed to be used with a cathode-ray oscillograph which lends itself to a variety of recording methods. The methods discussed include both the type where the time axis is obtained by sweeping the oscilloscope beam on a stationary film and where the time axis is obtained mechanically.

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A Novel Chirped Fiber Grating Sensor for Strain Detection

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.94-96.1222 ◽

2011 ◽

Vol 94-96 ◽

pp. 1222-1226

Author(s):

Hai Ying Yu ◽

Xiao Liu ◽

Tong Yu Liu ◽

Lin Suo ◽

Ling Song Yu

Keyword(s):

Light Intensity ◽

Temperature Compensation ◽

Low Cost ◽

Strain Sensor ◽

Fiber Grating ◽

Fiber Gratings ◽

Fiber Grating Sensor ◽

Chirped Fiber Grating ◽

Strain Detection ◽

Chirped Fiber Gratings

In this paper, a novel strain sensor based on chirped fiber grating with temperature compensation is presented. The proposed strain sensor uses double chirped fiber gratings. The temperature compensation exploit the principle that the wavelength shifts of these two chirped fiber gratings induced by temperature is consistent. This strain sensor is demodulated by the light intensity detection with low cost. Furthermore, the strain sensor is simulated in the end of this paper.

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Research on static and dynamic strain monitoring for a certain spacecraft based on optical fiber grating sensor

Fiber Optic Sensing and Optical Communication ◽

10.1117/12.2505510 ◽

2018 ◽

Cited By ~ 1

Author(s):

Yuxiang Luo ◽

Fei Shao ◽

Jiande Zhang ◽

Bo Xu ◽

Chunhui Guo ◽

...

Keyword(s):

Optical Fiber ◽

Dynamic Strain ◽

Fiber Grating ◽

Strain Monitoring ◽

Fiber Grating Sensor

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Dynamic Responses Measured by Optical Fiber Sensor for Structural Health Monitoring

Applied Sciences ◽

10.3390/app9152956 ◽

2019 ◽

Vol 9 (15) ◽

pp. 2956 ◽

Cited By ~ 7

Author(s):

Shiuh-Chuan Her ◽

Shin-Chieh Chung

Keyword(s):

Optical Fiber ◽

Dynamic Strain ◽

Fiber Grating ◽

Base Excitation ◽

Long Period ◽

Fiber Sensing ◽

Fbg Sensor ◽

Sensing System ◽

Optical Fiber Sensing ◽

Period Fiber Grating

An optical fiber sensing system integrating a fiber Bragg grating (FBG) sensor, a long-period fiber grating (LPFG) optical filter and a photodetector is presented to monitor the dynamic response of a structure subjected to base excitation and impact loading. The FBG sensor is attached to a test specimen and connected to an LPFG filter. As the light reflected from the FBG sensor is transmitted through the long-period fiber grating filter, the intensity of the light is modulated by the wavelength, which is affected by the strain of the FBG. By measuring the intensity of the light using a photodetector, the wavelength reflected from the FBG sensor can be demodulated, thus leading to the determination of the strain in the structure. To demonstrate its effectiveness, the proposed sensing system was employed to measure the dynamic strain of a beam subjected to mechanical testing. The mechanical tests comprised three load scenarios: base excitation by a shaker at resonant frequency, impact loading by a hammer and shock test on a drop table. To monitor the dynamic strain during the test and validate the accuracy of the measurement of the FBG sensor, strain gauge was used as reference. Experimental results show good correlation between the measurements of FBG sensor and strain gauge. The present work provides a fast response and easy-to-implement optical fiber sensing system for structural health monitoring based on real-time dynamic strain measurements.

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Influence of low-frequency parameter changes on nonlinear vibro-acoustic wave modulations used for crack detection

Structural Health Monitoring ◽

10.1177/1475921716689385 ◽

2017 ◽

Vol 17 (2) ◽

pp. 218-226 ◽

Cited By ~ 5

Author(s):

Bin Liu ◽

Zhiwei Luo ◽

Tie Gang

Keyword(s):

Crack Detection ◽

Crack Opening ◽

Low Frequency ◽

Intensity Variation ◽

Sine Wave ◽

Dynamic Strain ◽

Low Frequency Vibration ◽

Test Parameters ◽

Increased Sensitivity ◽

Acoustic Modulation

The use of vibro-acoustic modulation is an effective nonlinear and nondestructive approach to the detection and monitoring of cracks in fatigued, defective, and fractured materials. However, the vibro-acoustic modulation results strongly depend on choice of the testing parameters. To implement this technique for additional applications, the effect of variation in the test parameters must be well understood. This study investigates the influence of variation in the amplitude and frequency of pumping (low-frequency vibration) signals on the modulation. We apply two kinds of probing excitations, sine-wave and swept-signal excitations, and we measure the modulation intensity variation with changes in the relevant parameters to observe their influence on the modulations. Dynamic strain measurement of the crack area is utilized to analyze the relation between the degree of crack opening/closing and the modulation on the crack interface. The results indicate that the probing amplitude has little effect on the modulation, and furthermore, the sweep-signal excitation technique can be used to select the proper probing frequency. The results also indicate that there is a critical pumping strain value ( εc) for the crack samples. When the pumping strain reaches this critical value, the modulation reaches a maximum. However, the opening/closing area cannot increase any more even if the pumping amplitude further increases, and thus, the modulation does not change. The extent of the crack opening/closing also varies with the pumping frequency. Our results suggest that increased sensitivity to crack detection can be achieved with the use of the resonance frequency as the pumping frequency in vibro-acoustic modulation tests.

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Silver Cluster Formation in Implanted A12O3 Single Crystals

MRS Proceedings ◽

10.1557/proc-396-385 ◽

1995 ◽

Vol 396 ◽

Cited By ~ 3

Author(s):

F.L. Freire ◽

N. Broil ◽

G. Mariotto

Keyword(s):

Single Crystals ◽

Cluster Formation ◽

Low Frequency ◽

Silver Cluster ◽

Laser Frequency ◽

Implantation Dose ◽

Silver Clusters ◽

Linear Absorption ◽

Broad Absorption Band ◽

Depth Profiles

AbstractSingle crystals of sapphire were implanted at room temperature with 300 keV-Ag+. The metal precipitate was characterized by a multitechnique approach including RBS, optical absorption and Raman spectroscopy. RBS measurements were used to determine the depth-profiles of the implanted ions. Ag depth profiles, derived from RBS are in good agreement with the results predicted by Monte Carlo simulations. Linear absorption spectroscopy has been used to characterize the effects of the ion fluence on the optical properties of the metal colloids in the UV-Vis region. The broad absorption band due to the surface plasmon resonance shows an appreciable red-shift when the fluence of bombarding ions increases. Raman scattering from acoustic vibrations of the silver clusters progressively shifts toward the laser frequency with increasing implantation dose. From low-frequency Raman spectra an evaluation of the average size of metal aggregates was derived.

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